Tungsten-modified zirconia catalysts are known acidic solid oxide catalysts. U.S. Pat. No. 5,510,309 describes a method for preparing such a modified solid oxide catalyst by coprecipitating a Group IVB metal oxide with an oxyanion of a Group VIB metal.
The generation of acid activity in solid oxide catalysts such as tungsten-modified zirconia catalysts requires calcination of the catalyst at temperatures of about 800.degree. C. and higher. The high calcination temperature, however, causes a significant loss of surface area and results in a catalyst having a high particle density. Therefore, it is desirable to maximize the surface area and reduce the particle density of the catalyst, without adversely affecting the activity of the catalyst.
Ammonium sulfate has been used to prepare sulfated zirconia, a known acidic solid oxide catalyst, by impregnating zirconia with the ammonium sulfate, followed by calcination/activation at a temperature of about 600.degree. C. The sulfur content of the sulfated zirconia catalysts is in the range of 3 to 6 percent by weight.
No prior art reference, however, teaches a method for preparing an acidic solid oxide catalyst comprising the steps of combining sulfate and tungstate ions during coprecipitation, followed by removal of the sulfate ions to obtain an acidic solid oxide catalyst having a reduced particle density. For example, unlike the catalyst described in U.S. Pat. No. 4,918,041, the resultant catalyst of the present method is essentially free of sulfate ions.